Interfaces in Java (just read this article)

In Java, an interface is an abstract type that defines a set of abstract methods and constants (or no methods or constants). An interface is a convention that specifies the behavior that a certain type of object should have.

Here is some important information about Java interfaces:

1. Define interface :

   Use interfacethe keyword to define the interface.

   interface MyInterface {
         
         
       // 声明抽象方法
       void myMethod();
       
       // 声明常量（默认为 public static final）
       int MY_CONSTANT = 10;
   }
   

2. Implement interface :

   A class can implement one or more interfaces, implementsimplemented through the keyword.

   class MyClass implements MyInterface {
         
         
       @Override
       public void myMethod() {
         
         
           System.out.println("Implementing myMethod");
       }
   }
   

3. The difference between interface and abstract class :

   • Methods in interfaces are abstract by default and do not contain method bodies; abstract classes can contain abstract methods and concrete methods.
   • A class can implement multiple interfaces, but can only inherit from one class.
   • The fields in the interface are of public static finaltype by default, that is, constants; abstract classes can contain fields of various types.

4. Multiple inheritance of interfaces :

   An interface can inherit from multiple interfaces.

   interface InterfaceA {
         
         
       void methodA();
   }
   
   interface InterfaceB {
         
         
       void methodB();
   }
   
   interface InterfaceC extends InterfaceA, InterfaceB {
         
         
       void methodC();
   }
   

5. Default method :

   Java 8 introduced default methods of interfaces, which can provide default implementations of methods in interfaces.

   interface MyInterface {
         
         
       void myMethod();
       
       default void defaultMethod() {
         
         
           System.out.println("Default method implementation");
       }
   }
   

6. Static method :

   Java 8 also introduced static methods in interfaces.

   interface MyInterface {
         
         
       void myMethod();
       
       static void staticMethod() {
         
         
           System.out.println("Static method in interface");
       }
   }
   

7. Practical applications of the interface :

   • Interfaces are used to implement polymorphism, which allows different classes to have the same behavioral interface, but in different implementation methods.
   • An interface is a design convention used to describe what methods and constants a class should have.
   • The Java standard library uses interfaces extensively, such as java.util.Listinterfaces.

Interface is a very important concept in Java. It provides a way to organize and standardize the structure of code, and supports more flexible polymorphism.